how to fill second Column according to selection of first GridViewComboBoxColumn

Question

Wow, it took about 2 hours for me to find out this answer, well not good but usable and helpful :)

First, you have to change your groupColumn.DataSource to a BindingSource not a DataTable as in your code, because you need some PositionChanged event to notify when you select an item from a combobox in groupColumn. You know that DataGridViewColumn doesn't have any SelectedIndexChanged event. Second, I don't see any relationship between your Group and Services, the datasource of Services should have a field like GroupID, so that you can link between 2 columns. I suppose there is such a GroupID field. Your Services has an ID but I'm not sure if it's GroupID, it may be your ServiceID.

Recommended: I think you should change your groupColumn's and serviceColumn's DisplayStyle to DataGridViewComboBoxDisplayStyle.Nothing - it looks best to me.

I would like to explain my solution in the comment beside the code. Here is the code:

//Your code is modified a little.
var groupColumn = new DataGridViewComboBoxColumn();
groupColumn.DisplayStyle = DataGridViewComboBoxDisplayStyle.Nothing;
DataTable dtcategori = cb.GetAllDataCategori();
groupColumn.Name = "Group";
groupColumn.HeaderText = Resources.GroupName;
//Create a BindingSource from your DataTable
BindingSource bs = new BindingSource(dtcategori,"");
groupColumn.DataSource = bs;
bs.PositionChanged += (s,e) => {
   //Filter for items which have the selected GroupID
   ((DataTable)((DataGridViewComboBoxColumn)DataGridViewFactor.Columns["Services"]).DataSource).DefaultView.RowFilter =
                string.Format("GroupID='{0}'",((DataRowView)bs.Current).Row["ID"]);
   //Set the initial value of the corresponding cell in serviceColumn
   DataGridViewFactor.CurrentRow.Cells["Services"].Value = ((DataTable)((DataGridViewComboBoxColumn)DataGridViewFactor.Columns["Services"]).DataSource).DefaultView.ToTable().Rows[0]["Name"];
};
//-------------------------------------------
groupColumn.ValueMember = "ID";
groupColumn.DisplayMember = "Name";
groupColumn.Width = 100;
this.DataGridViewFactor.Columns.Add(groupColumn);

var serviceColumn = new DataGridViewComboBoxColumn();
serviceColumn.DisplayStyle = DataGridViewComboBoxDisplayStyle.Nothing;
//var categoriId = Convert.ToInt32(groupColumn.);
// DataTable dtServices = sb.ServiceGetById(categoriId);
DataTable dtServices = sb.GetAllDataServices();
serviceColumn.Name = "Services";
serviceColumn.HeaderText = Resources.Service;
serviceColumn.DataSource = dtServices;
serviceColumn.ValueMember = "ID";
serviceColumn.DisplayMember = "Name";
serviceColumn.Width = 100;

this.DataGridViewFactor.Columns.Add(serviceColumn);

//Because filtering this way can make some cell have a value which is not contained in 
//the DataGridViewComboBoxColumn.Items, we have to handle the DataError
private void DataGridViewFactor_DataError(object sender, DataGridViewDataErrorEventArgs e){
    //We're interested only in DataGridViewComboBoxColumn
    if(DataGridViewFactor.Columns[e.ColumnIndex] is DataGridViewComboBoxColumn){
        e.Cancel = true;
    }
}
//Because when you filter on a row, the DataGridViewComboBoxColumn.DataSource with
//the filtered DefaultView will apply on all the rows in the same 
//DataGridViewComboBoxColumn, we have to apply the filter for each row if it is selected
private void DataGridViewFactor_SelectionChanged(object sender, EventArgs e)
{            
        ((DataTable)((DataGridViewComboBoxColumn)DataGridViewFactor.Columns["Services"]).DataSource).DefaultView.RowFilter =
           string.Format("GroupID='{0}'", DataGridViewFactor.CurrentRow.Cells["Group"].Value);            
}
//Because when you filter on a row, the DataSource DefaultView of the groupColumn will
//be changed (limited to fewer items) and there will be cells in that column having 
//values which are not contained in the filtered items. Those cells will not be 
//displayed when you move the mouse over. This CellPainting event handler is to help 
//them look normal.
private void DataGridViewFactor_CellPainting(object sender, DataGridViewCellPaintingEventArgs e){
    if (e.RowIndex > -1 && e.ColumnIndex > -1)
    {
            if (e.Value != null)
            {
                e.Handled = true;
                e.PaintBackground(e.CellBounds, true);
                StringFormat sf = new StringFormat() { LineAlignment = StringAlignment.Center };
                e.Graphics.DrawString(e.Value.ToString(), DataGridViewFactor.Font, new SolidBrush(DataGridViewFactor.ForeColor), e.CellBounds, sf);
            }
    }
}

And that's all.

I hope it helps you!